Processes for stripping dyes from or decolorizing various materials are known in the art. For example, U.S. Pat. No. 4,227,881 discloses a process for stripping dyes from textile fabric which includes heating an aqueous solution of an ammonium salt, a sulfite salt and an organic sulfonate to at least 140 degree F. (60 degree C.) and adding the dyed fabric to the heated solution while maintaining the temperature of the solution. In addition to the costly heating and temperature maintenance step, this process has the drawback of producing fabric which after processing exhibits a remaining color depth. U.S. Pat. No. 4,783,193 discloses a process for stripping color from synthetic polymer products by contacting the colored polymer with a chemical system. The described process uses unstable dispersions of alkyl halides and aqueous solutions of bleaching/oxidizing agents to which specified quantities of acids and surfactant/wetting agents are added. Among the drawbacks are the use of potentially hazardous halogens and the special provisions required to prevent escape of vapors which could cause environmental harm. Further, the use of the chemical system may restrict or eliminate the polymeric material's recycleability. In general, processes which utilize harsh stripping agents destroy the usefulness of the colorant, thus generating a chemical waste stream that must be treated or disposed of in an environmentally conscious manner. These methods can also generate unremovable colorant fragments which limit the downstream recycleability and utility of the color-stripped material. The methods are not suitable for selectively removing dye from the surfaces only of the textile material.
It is known to decolorize and desize dyed cellulosic fabric utilizing ozone, for example U.S. Pat. No. 5,366,510 to Wasinger. Dyes for cellulosic fibers have five major color application categories designated specifically for this chemical fiber type. Direct, vat, sulfur and reactive, along with azoic combinations. This is in sharp contract to dyeing man-made fibers which include acetate, acrylic, modacrylic, nylon, polyester and polyurethane fibers which are chemically diverse, mostly hydrophobic and are colored by disperse dye application. The most important fibers, polyester, nylon and cellulose acetate are generally disperse dyed. Acrylic and modacrylic can be dyed with both basic and disperse dyes. On acrylic fibers disperse dyes do not build well.
Japanese Patent No. 02004068170 to Tashiro et al published March, 2004 discloses the decolorization of an amine copolymer of polyaspartate at high temperatures in water with a stream of ozone.
However, the reference fails to selectively decolorize only the colorant from the surface without any substantial decolorization of the colorant in the fibers of the textile.
U.S. Pat. No. 4,012,357 to Foulks et al discloses bleaching esters with ozone, peroxide, hypochlorite, bleaching clays and the like. The process is not selective in only treating plated colorant as provided by the present invention and does not disclose bubbling ozone in a liquid for a specific time or temperature.
In batch dyeing the dye particles become associated with the surface of the synthetic fibers and then penetrate directly into the synthetic fiber. However, some dyes have the tendency to plate the surface of the fibers such as polyester before the dye has an opportunity to penetrate the fiber. Problems occur when there is an excess of soluble dye or disperse dye in the dye bath due to the concentration of the dye present exceeding the Saturation solubility of the dye at the particular dye temperature so that the dye does not transfer into the fiber but plates on the surface. It would be desirable to dissolve the plated dye which leads to specks.
Some of the problem found is when there is a mixture of fibers and the rate of dyeing and the temperatures of dyeing differ for each fiber so that the dye does not dissolve or penetrate into the fiber but plates the surface.
The problems in the industry are found when utilizing vat dyeing or mainstream equipment such as jets, wenches, beams or package dyeing.
Because disperse dyes have no or limited solubility in water, some particulate disperse dye may occlude to the fiber surface after the dyeing phase is complete. Excess dye on fiber surfaces results in adverse results such as reduced wet-fastness, wash-fastness, sublimation and dry cleaning fastness as well as dulling of shade.
The usual practice for removing unwanted dyes is called reduction clearing and uses a bath of caustic soda and sodium dithionite and a surfactant. The ease of removal varies from dye to dye and in some cases the dye is only partially reduced and results in a dull color.
Ozone is a powerful oxidizing agent which in many cases destroys the chemical structure of the dye so as to make it soluble or completely decolorizes the dye.
Unwanted dye is not only found on fabrics or yarns but can occur when equipment is used for multiple tasks or to run different dye batches. Deposited or excess dye is difficult to remove from washers or other equipment because it can enter different cracks or crevices in the washer or other equipment or to appear later during a run of a different dye batch. It would be advantageous to be able to dissolve and remove or decolorize the residual dye before beginning another operation in the washer or in other textile working equipment.